Effect Of Minor Scandium On Microstructures And Mechanical Properties Of Spray Formed Al-Zn-Mg-Cu-Zr Alloy

This thesis mainly researched the microstructure examination and mechanicalproperties of spray formed Al-12Zn-2.6Mg-1.8Cu-0.18Zr-xSc（x=0,0.1,0.15,0.2）indepositional combination state, squeezed state and solution state by means ofmetallographic microscope, X-ray diffraction analysis(XRD) scanning electronmicroscope (SEM), energy spectrum analysis, Vickers hardness test, roomtemperature test and high temperature tensile test equipment, analyzing themicrostructure of ultra-high strength aluminum alloy and the Evolutional law afterthe process from spray formed base making to heat-treatment, and reveals thestrengthening mechanism of alloy to continuously improve the parameter evidence ofthe process of designing of ultra-high strength aluminum alloy by spray forming andheat-treatment in the purpose of improving those materials’ performance. The mainresults are as follows:I have made the Al-12Zn-2.6Mg-1.8Cu-0.18Zr-xSc（x=0,0.1,0.15,0.2）sprayformed bases of spray formed ultra-high strength aluminum alloy, Their tissue have adensity of95%~99%. which has a detailed surface without obvious hole andshrinkage cavity in the size of Φ220×260mm with prepared50kg supersonicatomization sedimentation equipment. Compared with the as-cast dendritic structure,spray forming are all paraxial with grain uniformity, significantly inhibited theobvious macrosegregation., mainly between10~50μm. As a result of the action ofSc elements, including Sc alloy microstructure is thining obviously. when the contentof Sc raised to0.15%,then becomes minimum of15μm. The second phase in thealloy is mainly composed by the second phase of net worked crystal boundary,intracrystalline acicular phase, intracrystalline globular phase and few massiveness.The second phase are mainly that MgZn2analysis by energy spectrum and X-ray diffraction analysis.As-deposited alloy after hot extrusion, bulky second phase was fully brokenand is uniformly distributed along the extrusion direction, hole and shrinkagecavity is eliminated, organization in the alloy achieve full densification, equiaxedgrain elongated along the extrusion direction, forming texture organization. Alloywith T6heat treatment for extrusion condition, heat treatment after showed excellentmechanical properties at room temperature and high temperature alloy, including0.15%Sc alloy mechanical properties of the best, the room temperature tensilestrength of804.1Mpa, elongation rate reached7.0%;150°C under the condition oftensile tensile strength of688Mpa, the elongation reached15.8%. Than excludingSc elements alloy, the right amount of Sc elements can make the mechanicalproperties of the alloy improved significantly.